"""
自定义分页组件
以后如果想要使用这个分页组件，你需要做如下几件事:


在视图函数中:
def pretty_list(request):
    # 1.根据自己的情况去筛选自己的数据
    queryset = models.PrettyNum.objects.all()

    # 2.实例化分页对象
    page_object = Pagination(request, queryset)

    context = {
        'queryset': page_object.page_queryset,  # 分完页的数据
        'page_string': page_object.html()  # 页码
    }
    return render(request, 'pretty_list.html', context)
在html页面中:
<nav aria-label="Page navigation" style="text-align: center">
        <ul class="pagination">
            <li>
                <a aria-label="Previous">
                    <span aria-hidden="true">&laquo;</span>
                </a>
            </li>
            {{ page_string }}
            <li>
                <a aria-label="Next">
                    <span aria-hidden="true">&raquo;</span>
                </a>
            </li>
        </ul>
    </nav>



"""
# 将字符串识别成安全的html
from django.utils.safestring import mark_safe


class Pagination(object):
    def __init__(self, request, queryset, page_size=10, page_param='page', plus=5):
        """
        :param request: 请求的对象
        :param queryset: 符合条件的数据(根据这个数据给他进行分页处理)
        :param page_size: 每页显示多少条数据
        :param page_param: 在URL中传递的获取分页的参数,
        :param plus: 显示当前页的 前或后几页(页码)
        """
        import copy
        query_dict = copy.deepcopy(request.GET)
        query_dict._mutable = True
        self.query_dict = query_dict
        self.page_param = page_param

        page = request.GET.get(page_param, "1")
        # 判断是否是十进制的数
        if page.isdecimal():
            page = int(page)
        else:
            page = 1
        self.page = page
        self.page_size = page_size

        self.start = (page - 1) * page_size
        self.end = page * page_size

        self.page_queryset = queryset[self.start:self.end]
        # 得到符合数据库规则的条数
        total_count = queryset.count()
        # 计算出总页码
        total_page_count, div = divmod(total_count, page_size)
        if div:
            total_page_count += 1
        self.total_page_count = total_page_count
        self.plus = plus

    def html(self):
        # 计算出，显示当前页的前5页，后5页

        if self.total_page_count <= 2 * self.plus + 1:
            # 当数据量足够小的时候,都没有达到11页
            start_page = 1
            end_page = self.total_page_count
        else:
            # 数据库中的数据比较多 > 11页
            if self.page <= self.plus:
                # 当前页<5时(小极值)
                start_page = 1
                end_page = 2 * self.plus + 1
            else:
                # 当前页>5
                # 当前页+5>总页码
                if (self.page + self.plus) > self.total_page_count:
                    start_page = self.total_page_count - 2 * self.plus
                    end_page = self.total_page_count
                else:
                    start_page = self.page - self.plus
                    end_page = self.page + self.plus

        # 展示当前页数对应的那几条数据
        # queryset = models.PrettyNum.objects.all().order_by("-level")

        # 页码
        page_str_list = []

        self.query_dict.setlist(self.page_param, [1])
        # 首页
        page_str_list.append('<li><a href="?{}">首页</a></li>'.format(self.query_dict.urlencode()))
        # 上一页
        if self.page > 1:
            self.query_dict.setlist(self.page_param, [self.page - 1])
            prev = '<li><a href="?{}">上一页</a></li>'.format(self.query_dict.urlencode())
        else:
            self.query_dict.setlist(self.page_param, [1])
            prev = '<li><a href="?{}">上一页</a></li>'.format(self.query_dict.urlencode())
        page_str_list.append(prev)

        # 页面
        for i in range(start_page, end_page + 1):
            self.query_dict.setlist(self.page_param, [i])
            if i == self.page:
                ele = '<li><a style="background-color: lightgrey" href="?{}">{}</a></li>'.format(self.query_dict.urlencode(),i)
            else:
                ele = '<li><a href="?{}">{}</a></li>'.format(self.query_dict.urlencode(), i)
            page_str_list.append(ele)

        # 下一页
        if self.page < self.total_page_count:
            self.query_dict.setlist(self.page_param, [self.page + 1])
            prev = '<li><a href="?{}">下一页</a></li>'.format(self.query_dict.urlencode())
        else:
            self.query_dict.setlist(self.page_param, [self.total_page_count])
            prev = '<li><a href="?{}">下一页</a></li>'.format(self.query_dict.urlencode())
        page_str_list.append(prev)
        # 尾页
        self.query_dict.setlist(self.page_param, [self.total_page_count])
        page_str_list.append('<li><a href="?{}">尾页</a></li>'.format(self.query_dict.urlencode()))

        page_string = mark_safe("".join(page_str_list))
        return page_string
